Structure of Monocercomonas sp. as Revealed by Electron Microscopy*

SYNOPSIS. Monocercomonas shares many fine-structural features with all other trichomonads. These include the basic arrangement of the kinetosomes as well as of the recurrent and 3 anterior flagella. The pelta-axostyle complex and the parabasal apparatus, i.e. the Golgi complex and the periodic filaments, also conform to the trichomonad pattern. Of interest with regard to the crucial evolutionary position of Monocercomonas, considered to represent the most primitive trichomonad type, is the fact that it has some structures in common with other Monocercomonadidae and Trichomonadinae and others in common with Devescovinidae and Tritrichomonadinae. Among the former organelles are the marginal lamella and the costal base, and among the latter, the comb-like organelle situated between the infrakinetosomal body and parabasal filament 2 as well as the infrakinetosomal body. No traces of either costa or undulating membrane have been noted, but a complex structure homologous to the marginal lamella of Hypotrichomonas and Trichomonadinae is found underlying the short anteriormost portion of the recurrent flagellum that is attached to the body surface. Observations of sections of selected division stages indicate the potential of parental kinetosomes #1 and #3 to become daughter kinetosome #2.     

Fine Structure of the Mastigont System in Tritrichomonas foetus (Riedmüller)*

SYNOPSIS. Tritrichomonas foetus shares many fine-structural features with the previously described genera of the subfamily Trichomonadinae. These include the arrangement and structure of the kinetosomes, of most rootlet filaments, including the sigmoid filaments of kinetosome #2, as well as those of the parabasal apparatus and of the pelta-axostyle complex. On the other hand, this species, and presumably all other Tritrichomonas augusta-type flagellates, differ from Trichomonadinae in certain important details. Among the features which T. foetus does not share with Trichomonadinae are the fine structure of the costa and of the undulating membrane, as well as several organelles not found in the latter subfamily. The costal base of Trichomonadinae is replaced in T. foetus and other Tritrichomonadinae by a comb-like structure, extending between the costa and the infrakinetosomal body. The suprakinetosomal body, connected to kinetosome #2 in the region of attachment of the sigmoid filaments, and the infrakinetosomal body, which appears to contribute to the proximal marginal lamella, are organelles evidently restricted to Tritrichomonadinae. The undulating membrane consists of 2 parts. The proximal part is a fold-like differentiation of the dorsal body surface, the dorsal part of which contains the proximal marginal lamella. The distal part of the undulating membrane, with no obvious physical connection to the fold, encloses the distal marginal lamella in its ventral, and the microtubules of the recurrent flagellum in its dorsal area. The organelle of T. foetus which by its size, certain structural characteristics, and relationship with the undulating membrane and some organelles, including the paracostal granules, is analogous to the costa of Trichomonadinae and of Trichomitopsis termopsidis (subfamily Tritrichomonadinae), conforms in the structure of its periodic cross-striations to that of the parabasal filaments of the latter organisms; its origin corresponds closely to that of parabasal filament 2 of Trichomonadinae.     

Fine Structure of the Mastigont System in Tritrichomonas muris (Grassi)*

SYNOPSIS. Tritrichomonas muris shares many fine-structural details with the previously described members of the family Trichomonadidae, and especially with the organisms belonging to the subfamily Tritrichomonadinae. Among the features which T. muris has in common with all Trichomonadidae and in all probability with other Trichomonadida are the arrangement and structure of: the kinetosomes; many rootlet filaments, including the sigmoid filaments of kinetosome #2; the parabasal apparatus; and the pelta-axostyle complex. The structures which T. muris-type flagellates share with other Tritrichomonadinae, and especially with Tritrichomonas augusta-type species (including T. foetus), but not with Trichomonadinae that have been studied to date, are: the Type A costa; a comb-like structure, which appears to have replaced the costal base of Trichomonadinae and of Hypotrichomonas; the suprakinetosomal body, rudimentary in T. muris; and the infrakinetosomal body. The undulating membrane, like that of T. augusta-type organisms, consists of a proximal and a distal part. The proximal part, which contains the proximal marginal lamella, is less developed in T. muris than in T. augusta-type flagellates, being represented by a relatively low ridge for the entire length of the organism. The distal part of the membrane in T. muris, on the other hand, is more highly developed; it is a heavy cord, with a distal marginal lamella which consists of a large triangular organelle having a highly ordered structure and 2 less well defined cords distal to this organelle. The tubules of the recurrent flagellum occupy the area distal to the cords. The sigmoid filaments of kinetosome #2, unlike those of other Trichomonadidae examined to date, extend posteriorly to the peltar-axostylar junction; they seem to terminate within the cytoplasm near, but not connected to the axostyle. In addition to the Type A costa, there is a small rootlet filament, which appears to be homologous to the rudimentary costa noted in Hypotrichomonas. Some of the paraxostylar and paracostal granules consist of an outer, relatively dense layer and an inner “core” of moderate density; between the 2 there is a lucent ring. The discussion deals in some detail with the possible nature of the paraxostylar and paracostal granules in trichomonads. The taxonomic status of Tritrichomonas cricetus (Wantland) [Tritrichomonas criceti (Wantland) emend. Levine] and Trichomonas criceti Ray & Sen Gupta is discussed in an appendix; it is concluded that both of these names are synonyms of T. muris (Grassi).     

Structure of Pentatrichomonas hominis (Davaine) as Revealed by Electron Microscopy*

SYNOPSIS. Fine structure of Pentatrichomonas hominis is described in the light of previous light microscopic findings. The relationships among kinetosomes #1-#4 and R are like those previously reported orhomonas gallinae, and the same is true of the rootlet filaments associated with the several kinetosomes. The kinetosome (I) of the independent flagellum is situated just behind the reflection of the sigmoid filaments of kinetosome #2 onto the pelta and parallels these filaments for a considerable distance. The peltaraxostylar junction consists of 3 layers: the capitulum of the axostyle (outer, the pelta (intermediate, and the sigmoid rootlets of kineto some #2 (inner). The pelta overlaps the axostylar capitulum to a variable extent. The parabasal body consists of elongate and flattened cisternae of smooth endoplasmic reticulum surrounded by numerous small vesicles. There are 2 typically cross-striated parabasal filaments, filament 2 probably contributing most, if not all, the material to the slender, periodic organelle that underlies the parabasal body and usually does not extend far beyond the posterior end of the nucleus. The periodic costa is paralleled by paracostal granules, but there are few, if any, paraxostylar granules. The ultrastructure of the costa appears to be a network of flattened hexagons, with a single fibril projecting thru each of the hexagonal areas. The major cross-striations are made up largely of densely-stained filaments which are occasionally cut in cross section. The undulating membrane consists of a cytoplasmic fold extending from the dorsal surface of the organism and of the attached part of the recurrent flagellum, which is closely applied to the fold. The segment of the membrane dorsal to the flagellum, presumably the “accessory filament,” contains the marginal lamella, a membrane folded upon itself and with periodicity virtually indistinguishable from that of the rootlet filament of kinetosome #1.     

Structure of Hypotrichomonas acosta (Moskowitz) (Monocercomonadidae,Trichomonadida) as Revealed by Electron Microscopy*

SYNOPSIS. The fine structure of Hypotrichomonas acosta resembles in many respects that of Trichomonadidae, and especially of members of the sub-family Trichomonadinae which have been examined to date by electron microscopy. In addition, the flagellate has certain ultrastructural differences from the latter organisms, some of which are of phylogenetic significance. Among these, the structure of the undulating membrane and the apparently occasional presence of a fine filament which may be considered as homologous to the costa of Trichomonadidae are the most important. The undulating membrane is represented by a rather low and otherwise poorly developed dorsal cytoplasmic fold with an ill-defined distal marginal lamella; the recurrent flagellum is applied near the dorsum of the fold. In a very few preparations a relatively short filament, of a diameter falling below the resolution limits of light microscope, is seen in a position which corresponds to that of the costa of Trichomonadidae. The identity of the filament as a probable rudimentary costa is supported also by the character of its periodicity. The rare appearance of the rudimentary costa among hundreds of sections may be explained either by its minute dimensions or by its absence from many hypotrichomonads. Other structures recorded for the first time in trichomonads are: the fine filamentous connections of the axostylar microtubules; the branching of parabasal filament 2; and the unusually organized, perhaps helical, polysomes, which are found in addition to the ribosomal complexes associated with the endoplasmic reticulum and commonly found in trichomonads. A detailed analysis of interconnections among various mastigont structures is presented and several kinds of cytoplasmic inclusions are described. H. acosta is of interest in the study of the nuclear envelope and presence of nuclear pores, which are numerous and conspicuous in this flagellate. The fine structure of the hypotrichomonad is discussed in relation to that of other trichomonads and in some instances to that of other protozoa.     

Fine-Structural Changes Associated with Pseudocyst Formation in Trichomitus batrachorum*

SYNOPSIS. Several fine-structural changes were observed during formation of the so-called pseudocysts of Trichomitus batrachorum grown in an agar-free medium. Among these changes the most frequent were those of the undulating membrane complex. Internalization of the marginal lamella combined with disappearance of the fin-like, membranous dorsal fold occurred with the highest frequency. In many organisms these alterations were accompanied by internalization of the recurrent flagellum, which, however, remained external in other, presumably earlier stages of pseudocyst formation. In some of the internalized and even still external recurrent flagella the microtubules were in various states of disassembly. The often distended flagellar membrane enclosed large accumulations of filaments 5 nm in diameter. Internalization of the anterior flagella also was noted. Changes similar to those characteristic of the recurrent flagella were not seen, however, among the microtubules of the anterior flagella or among those of the pelta or the axostyle.     

Developmental studies on the loricate choanoflagellateStephanoeca diplocostata Ellis. V. The cytoskeleton and the effects of microtubule poisons

Summary InStephanoeca diplocostata microtubules are located in four positions namely: within the flagellar axoneme; just beneath the plasmalemma; associated with the silica deposition vesicles (SDVs) during early stages of costal strip deposition; and in the mitotic spindle. At the anterior end of the cell the 50–60 peripheral microtubules, which are organized more or less parallel to the long axis of the cell, converge around the base of the emergent flagellum. A short second flagellar base is positioned between the nucleus and the base of the emergent flagellum. Developing costal strips are located individually within SDVs in the peripheral cytoplasm. During the early stages of silica deposition each SDV is curved and subtended longitudinally on its concave side by two microtubules. When a costal strip has achieved sufficient rigidity to withstand bending the SDV-associated microtubules are depolymerized. Treatment of exponentially growing cells with sublethal concentrations of microtubule poisons, such as colchicine, podophyllotoxin, griseofulvin andVinca alkaloids depresses growth. Treatment with these drugs also affects the length and morphology of developing costal strips perhaps by interfering with the shaping and supporting functions of SDV-associated microtubules. Instead of being long and crescentic with a standard radius of curvature, costal strips of treated cells are usually short and misshapen, with irregular bends. After drug treatment, juveniles produced as a result of cell division do not develop flagella but can still assemble a lorica although it is usually misshapen. The role of microtubules and microfilaments in lorica production is discussed.     

Structure of trichomonads as revealed by scanning electron microscopy.

A scanning electron microscope (SEM) study of Hypotrichomonas acosta (Moskowitz), Trichomonas vaginalis Donné, Pentatrichomonas hominis (Davaine), and Tritrichomonas foetus (Riedmüller) provided new information about the structure of the periflagellar canal; emergence of the flagella from the cell body; structure of the undulating membrane; and position, shape, and size of the pelta. Of special interest were the spatial relationships of the attached part of the recurrent flagellum and the accessory filament in Hypotrichomonas and in the members of Trichomonadinae, i.e. Trichomonas and Pentatrichomonas.     

Structure of Trichomonads as Revealed by Scanning Electron Microscopy*†

SYNOPSIS.
A scanning electron microscope (SEM) study of Hypotrichomonas acosta (Moskowitz), Trichomonas vaginalis Donné. Pentatrichomonas hominis (Davaine), and Tritrichomonas foetus (Riedmüller) provided new information about the structure of the periflagellar canal: emergence of the flagella from the cell body; structure of the undulating membrane; and position, shape, and size of the pelta. Of special interest were the spatial relationships of the attached part of the recurrent flagellum and the accessory filament in Hypotrichomonas and in the members of Trichomonadinae, i.e. Trichomonas and Pentatrichomonas.     

A Freeze-Fracture Electron Microscope Study of Trichomonas vaginalis Donné and Tritrichomonas foetus (Riedmüller)1

Two strains of Trichomonas vaginalis, JH162A, with low pathogenicity, and Balt 44, with high pathogenicity, as well as one highly pathogenic strain, KV-1, of Tritrichomonas foetus were studied by freeze-fracture electron microscopy. The protoplasmic faces (PFs) of the cell membranes of all three strains of both species had similar numbers of intramembranous particles (IMPs); however, the particles in the external faces (EFs) of these membranes were least abundant in Trichomonas vaginalis strain Balt 44 and most numerous in those of strain JH162A of this species. In Tritrichomonas foetus strain KV-1 the number of IMPs in the EF was close to but somewhat lower than that in the mild strain of the human urogenital trichomonad. In both species, the anterior, but not the recurrent, flagella had rosette-like formations, consisting of ～9 to 12 IMPs on both the PFs and EFs. The numbers and distribution of the rosettes appeared to vary among different flagella and in different areas of individual flagella of a single organism belonging to either species. The freeze-fracture electron micrographs provided a more complete understanding of the fine structure of undulating membranes of Trichomonadinae, as represented by Trichomonas vaginalis, and of Tritrichomonadinae (the Tritrichomonas augusta-type), as exemplified by Tritrichomonas foetus, than was gained from previous transmission and scanning electron microscope studies. Typically three longitudinal rows of IMPs on the PF of the recurrent flagellum of Trichomonas vaginalis were noted in the area of attachment of this flagellum to the undulating membrane. The functional aspects of the various structures and differences between certain organelles revealed in the two trichomonad species by the freeze-fracture method are discussed.     

Structure and Life Cycle of Trypanoplasma beckeri sp. n. (Kinetoplastida), a Parasite of the Cabezon,Scorpaenichthys marmoratus,in Oregon Coastal Waters*,†

SYNOPSIS. Structure of Trypanoplasma beckeri sp. n. from the cabezon, Scorpaenichthys marmoratus (Ayres), is described from living specimens and from both Giemsa-, and protargol-stained smears. Flagellates from fish blood were usually long and slender, averaging 109.0 × 6.5 fan. The anterior flagellum averaged 8.5 μm; the recurrent flagellum bordered the body and terminated as a very short free flagellum, 2.5 μm long on the average. No true undulating membrane was observed, but in living individuals the recurrent flagellum undulated rapidly near its point of origin. The oval nucleus, averaging 8.5 × 4.0 μm, was located near the anterior cad of the body. An argentophilic, aciculum-like structure appeared to connect the nucleus to the area at the base of the flagella. The kinetoplast was not observed in fish blood forms. On the basis of laboratory experiments, the leech, Malmiana diminuta Burreson, was ascertained to be the vector for T. beckeri. Upon entry into the leech, flagellates became rounded, and division commenced within a few hours. Division continued for ?48 h and the flagellates became progressively smaller until reaching a length of ?10.0 μm. After 72 h they were found in high numbers in the proboscis sheath and also in the anterior crop of the leech. When infected leeches fed on an uninfected fish, flagellates were first observed in the fishes’ peripheral circulation 8 days later.     

Motion of the Longitudinal Flagellum in Ceratium tripos (Dinoflagellida): A Retractile Flagellar Motion1

The longitudinal flagellum of Ceratium tripos moves in two dissimilar ways: undulation and retraction. The undulatory wave is planar and has a wavelength of 74.3 ± 9.6 μm and an amplitude of 14.2 ± 2.3 μm in sea water. The beat frequency is 30 Hz at 20°C, pH 8.0. The retractile motion is unique to Ceratium and is triggered by mechanical stimulation on the cell body, especially at the tip of the apical horn. When it retracts, the longitudinal flagellum folds every 4–5 μm along the flagellum. Cinematographic study showed that the flagellum folded from tip to base and was finally installed into the sulcus, a groove on the ventral side of the cell. This motion is completed in sea water within 28 msec. The retracted flagellum then re-extends and restores the undulation within a few seconds. The flagellum unfolds in the proximal portion first, then the distal, and finally the middle portion. Fixation always triggers the retraction. Scanning electron microscopy showed that the flagellum is folded and secondarily twisted in a helix. A new fiber in addition to the flagellar axoneme was found in the retracted flagellum by phase microscopy. This fiber (R-fiber) seems to contract during the retraction to fold the flagellum.     

Tritrichomonas foetus: Fine Structure of Freeze-Fractured Membranes1

ABSTRACT. Freeze-fracture techniques reveal differences in fine structure between the anterior three flagella of Tritrichomonas foetus and its recurrent flagellum. The anterior flagella have rosettes of 9–12 intramembranous particles on both the P and E faces. The recurrent flagellum lacks rosettes but has ribbon-like arrays of particles along the length of the flagellum, which may be involved in the flagellum's attachment to the cell body. This flagellum is attached to the membrane of the cell body along a distinct groove that contains few discernible particles. Some large intramembranous particles are visible on the P face of the cell body membrane at the point where the flagellum emerges from the cell body. The randomly distributed particles on the P and E faces of the plasma membrane have a particle density of 919/μm² and 468/μm² respectively, and there are areas on both faces that are devoid of particles. Freeze-fracture techniques also reveal numerous fenestrations in the membrane of the Golgi complex and about 24 pores per μm² in the nuclear. membrane.     

CYTOLOGY AND ULTRASTRUCTURE OF CHLORARACHNION REPTANS (CHLORARACHNIOPHYTA DIVISIO NOVA,CHLORARACHNIOPHYCEAE CLASSIS NOVA)1

The green amoeboid cells of Chlorarachnion reptans Geitler are completely naked and each contains a central nucleus, several bilobed chloroplasts each with a central projecting pyrenoid enveloped by a capping vesicle, several Golgi bodies, mitochondria with tubular cristae, extensive rough ER, and a distinct layer of peripheral vesicles. Complex extrusome-like organelles occur rarely in both the amoeboid and flagellate stages. The only organelles entering the reticulopodia are mitochondria, but microtubules are also present. The chloroplasts contain chlorophylls a and b, but histochemical tests suggest that the carbohydrate storage product probably is not a starch. The chloroplast lamellae are composed of one to three thylakoids or form deep stacks. A girdle lamella and interlamellar partitions are absent. Each chloroplast is bounded by either four separate membranes, a pair of membranes with vesicular profiles between them, or three membranes; all three arrangements may occur in the same chloroplast. A periplastidal compartment occurs near the base of the pyrenoid where there are always four surrounding membranes. The compartment has a relatively dense matrix and contains ribosome-like particles and small dense spheres; it extends over and into a deep invagination in the pyrenoid where its contents are enclosed in a double-membraned envelope which is penetrated by wide pores. The zoospores are ovoid and each bears a single laterally inserted flagellum which appears to be wrapped helically around the cell body during swimming. The flagellum lies in a groove in the cell surface and bears fine lateral hairs. Neither a second flagellum or vestige of one, nor an eyespot, is present. A single microtubular root and a larger homogeneous root run from the flagellar base parallel to the emerging flagellum, between the nuclear envelope and the plasmalemma. In the simple flagellar transition region, fine filaments connect adjacent axonemal doublets. A detailed comparison of C. reptans with all other algal taxa results in the conclusion that it must be segregated in the new class Chlorarachniophyceae, the only class in the new division Chlorarachniophyta. The possibility that C. reptans evolved from a symbiosis between a colorless amoeboid cell and a chlorophyll b- containing eukaryote is considered, but the possible affinities of the symbiont remain enigmatic. The implications of the unique chloroplast structure of C. reptans for current hypotheses concerning the origin of chloroplasts are discussed.     

Tritrichomonas mobilensis n. sp. (Zoomastigophorea: Trichomonadida) from the Bolivian Squirrel Monkey Saimiri boliviensis boliviensis1

ABSTRACT. A trichomonad flagellate, Tritrichomonas mobilensis n. sp., is described from the large intestine of the squirrel monkey, Saimiri boliviensis boliviensis. The organism has a lanceolate body 7–10.5 μm in length; a well developed undulating membrane; a stout, tubular axostyle with periaxostylar rings that terminate in a cone-shaped segment projecting from the posterior end of the cell; and a moderately wide costa. The anterior flagella are about as long as the body, and the recurrent flagellum is of the acroneme type. All its characteristics suggest that the new species belongs in the Tritrichomonas augusta type of the subfamily Tritrichomonadinae.     

Flagellar biosynthesis exerts temporal regulation of secretion of specific Campylobacter jejuni colonization and virulence determinants

The Campylobacter jejuni flagellum exports both proteins that form the flagellar organelle for swimming motility and colonization and virulence factors that promote commensal colonization of the avian intestinal tract or invasion of human intestinal cells respectively. We explored how the C. jejuni flagellum is a versatile secretory organelle by examining molecular determinants that allow colonization and virulence factors to exploit the flagellum for their own secretion. Flagellar biogenesis was observed to exert temporal control of secretion of these proteins, indicating that a bolus of secretion of colonization and virulence factors occurs during hook biogenesis with filament polymerization itself reducing secretion of these factors. Furthermore, we found that intramolecular and intermolecular requirements for flagellar‐dependent secretion of these proteins were most reminiscent to those for flagellin secretion. Importantly, we discovered that secretion of one colonization and virulence factor, CiaI, was not required for invasion of human colonic cells, which counters previous hypotheses for how this protein functions during invasion. Instead, secretion of CiaI was essential for C. jejuni to facilitate commensal colonization of the natural avian host. Our work provides insight into the versatility of the bacterial flagellum as a secretory machine that can export proteins promoting diverse biological processes.     

Furcohaptor cynoglossi n. g., n. sp., an ancyrocephaline monogenean gill parasite with a bifurcate haptor and a note on its adhesive attitude

An ancyrocephaline monogenean,Furcohaptor cynoglossi n. g., n. sp., is described from the gills of the marine teleost flatfishCynoglossus macrostomus caught off the coast of Kerala State in India. The parasite is also recorded onC. puncticeps. The haptor divides to form two elongated and slender haptoral arms, each bearing at the distal end a cluster of relatively small sclerites, comprising the following: two hamuli, one of which is rod-shaped and the other of typical hooked shape; a bar articulating with the typical hamulus; five marginal hooklets of typical shape, each with a domus; a sixth marginal hooklet which is shorter and more slender than the others and lacks a domus. This sixth marginal hooklet is hard to locate in some individuals. The haptoral arms embrace a primary gill lamella, their distal hook-bearing regions meeting or overlapping on the side of the lamella opposite to the parasite's body. Species of the genusBifurcohaptor Jain, 1958 differ in that two of the hamuli are greatly enlarged and support the haptoral arms.     

Glossomastix chrysoplasta n. gen., n. sp. (Pinguiophyceae), a new coccoidal, colony-forming golden alga from southern Australia

Glossomastix chrysoplasta gen. et sp. nov. is described from cultures isolated from sandstone rubble, Sorrento Back Beach, Mornington Peninsula, Victoria, Australia. The alga forms wall‐less, coccoidal vegetative cells that congregate in mucilaginous colonies and reproduce by successive bipartition. Plastids have girdle lamellae and partially embedded pyrenoids that are traversed by cytoplasmic channels. Zoospores are uniflagellate and swim poorly; a narrow lingulate pseudopod provides their primary form of motion. The single flagellum, which lacks hairs, a flagellar swelling, and autofluorescence, is the equivalent of the posterior flagellum in other golden algae. The anterior flagellum is absent; the basal body with which it would normally be associated is blind. The flagellar apparatus has two basal bodies, three microtubular roots, and a rhizoplast. The posterior (elder) basal body has a transitional helix that is proximal to the basal plate. Glossomastix chrysoplasta, placed in the Pinguiophyceae on the basis of molecular sequence and biochemical data, shares some ultrastructural features with other members of the class, especially Polypodochrysis teissieri, which has similar zoospores, but it also differs from other pinguiophytes in many respects. Glossomastix chrysoplasta is the pinguiophyte with, on average, the largest cells (exclusive of external materials), and it is the only one with a colonial habit.